Fuel cells have been proposed as a power source for electric vehicles and other applications. An exemplary fuel cell has a membrane electrode assembly (MEA) with catalytic electrodes and a proton exchange membrane (PEM) sandwiched between the electrodes. Water (also known as product water) is generated at the cathode electrode based on the electrochemical reactions between hydrogen and oxygen occurring within the MEA. Efficient operation of a fuel cell depends on the ability to provide effective water management in the system, and more specifically to control transport of water away from generation sites on the cathode, and to recover and recycle water in the system.
The physical state of the product water generated in the MEA depends on the temperature and pressure at which the electrochemical reaction occurs. Generally the product water will be vapor at higher temperatures and lower pressures, and liquid at lower temperatures and higher pressures. Therefore, it is possible that the product water exists as liquid when the fuel cell stack is cooler, and gradually transitions to water vapor when the stack is at higher operating temperatures.
At full operating temperature, excess heat must be removed from the system. The PEM is often sensitive to high temperatures, such that the fuel cell operating conditions must be maintained below these degradation temperatures. Present methods of removing heat from the fuel cell include a coolant loop that circulates between plates within a bipolar plate assembly. This cooling system is physically separated from the fuel cell operations and relies on thermal conductivity of the metal elements, or barriers, to transfer heat into the coolant, and constant pumping to provide the necessary circulation. The coolant is a heat sink and can be subsequently regenerated or removed from the cooling loop. There is a need to optimize fuel cell performance by cooling a fuel cell while eliminating such coolant loops and improving the management of water.